Lecture 10/25 & 10/28 Flashcards
Test 4
T/F: purkinje fibers doesn’t have a lot of fast Na+ channels
F
Has lots of them
Repolarization is done _______ in the epicardium in the ventricles. The endocardium _________ to repolarize.
quicker/sooner
takes longer
Describe an Atrial muscle AP
Visually between a slow (SA) and fast (Ventricles) AP
Phase 0 is straught up like ventricles
AP is short like SA
This is d/t atria only contracting for a short period of time and not having to pump against a high resistance because the atria walls are thin
T/F: the heart uses neurotransmitters to permit AP
F
Gap junctions
Whats the easiest thing to go through the gap junction? What all can go through there?
Na+
Ca++ – bigger, therefore slower –> slower for AP
What is a con of gap junctions in the heart?
They are bidirectional
If there’s an atomic pacemaker generating AP in parts of the heart that it shouldn’t be, that AP can travel forward/backwards to a cell that isnt finished resetting and cause life threatening arrthymias (Ex. T-on-T; R-on-T)
What helps prevent re-entry rhythms?
Absolute refractory period
If an AP hits the cell while its in absolute refractory period, it wont generate an AP
What happens if an AP hits a cell while it’s in the relative refractory period?
Odd AP –> heart wont pump right
Which leads look at electrical current in the frontal plane?
3-leads
augmented leads
Frontal plane is also called ________
coronal plane
In 3 leads: Describe the leads that are on each limb
R arm: 2 neg
L foot: 2 positives
L arm: 1 neg/1pos
The 3 leads setup forms a _____ degree triangle
60
In a 3-Lead set up: Describe lead/electrode placement
Lead I: Horizontal
Positive L arm; Negative R arm
Lead II: Aimed toward L foot
Positive L foot; Negative R arm
Lead III: Aimed toward R foot
Positive L foot; Negative L arm
In 3-lead, which lead has the best view and why?
Lead II
Lead II (+) lead is aimed at L foot at 60 degrees which is almost the same as the mean electrical axis of 59 degrees
Who is Einthoven?
Dutch scientist from Europe
What are the 3 things we need for an EKG to work?
Leads
Recorder
Amplifier (makes it easier for recorder to pick up things)
The mean axis is ____ and is pointed to the _______
59 degrees
L foot
Which lead is similar to the mean axis?
Lead II
What is Right deviation?
Anything that shifts the heart greater than 59 degrees to the right.
What is a left deviation?
Anything that shifts the heart less than 59 degrees to the left.
What are some conditions that can make your heart deviate?
BBB
Big lungs from COPD
How does breathing effect your mean axis?
Deep breath in = shift axis to R
Postive angles are ________. Negative angles are ___________.
Clockwise
Counterclockwise
Ex) 60 degrees = -300 degrees
Describe the walls of the ventricles
R wall thinner than L wall
R wall only has to pump against resistance of pulmonary circulation
How does depolarization work in the ventricles?
L BB –> R BB –> L & R Ventricles endocardium –> to epicardium
If we could see atria repolarization, what would it be?
Negative deflection
Describe atria depolarization
Similar to ventricle depolarization
Toward L foot –> positive deflection lead II
What atria depolarizes fastest?
R atria
Describe Einthoven’s Deconstructed triangle
pulled apart and able to plot on a graph and intersect at a midpoint
Lead I: 0 degrees + / 180 (-)
Lead II: 60 (+) / 240 (-)
Lead III: 120 (+) / 300 (-)
What is Einthoven’s Law?
Net deflection in:
Lead I + Lead III = Lead II
How does lead I & lead III compare to lead II?
In a healthy heart, deflections will be smaller
If I need something outside of a frontal view, I need _________ leads
Precordial
When do you not see a deflection in lead I?
When this mean axis is perpendicular to lead I
Straight up/down
How do you find the net deflection in a QRS?
- Draw a line from the beginning of P wave across EKG
- Anything above that in QRS is positive deflection; below is negative
- Subtract the negative deflection from positive deflection.
If the mean axis is 60, what can we assume?
The net deflection in lead I & III are equal (equal vectors)
What does augmented leads view?
frontal electrical current (coronal)
aV____ means…
lowercase a = augmented
V = voltage
letter after is the location of the (+) electrode
In augmented leads: describe lead/electrode placement
aVR: R arm (+) / average LL/LA (-)
Majority deflections negative, lead used the least
-points to R arm
aVF: L foot (+) / average RA/LA (-)
-points straight down
aVL: L arm (+) / average RA/LL (-)
-points to L arm
What angle are the augmented leads?
aVR: 210 degrees
aVL: -30
aVF: +90
Which lead dont we use much? why?
aVR
(+) electrode at R arm; deflection almost always inverted
Which augmented leads are we more likely to see normal deflections in?
aVL and aVF
positive electrodes on the right and bottom so able to measure electricity from R –> L
Which leads are closest to chest? What does this mean?
Precordial Chest leads
Bigger deflections overall
How many precordial leads are there? How would you describe them?
6
They are all positive leads
V1-2: sternum leads
V3-4: anterior leads
V5-6: lateral leads
Where do you place the Precordial leads?
V1: R sternum/septum 4th ICS
V2: L sternum/septum 4th ICS
V3: between 2&4
V4-6: L lateral 5th ICS
Where is the negative electrode in precordial leads?
The average (-) in the standard 3 leads on RA/LA/LL
What are you able to see in V1? How does this show up in an EKG?
Top R of heart
Large (-) deflection for QRS; inverted P-wave
Describe the V2 lead
QRS probably negative (-)
This lead in the middle of the heart
Used most to see if posterior/anterior injury
What lead is used to Dx posterior/anterior injuries?
V2
If current is moving toward V2 it is an _________ injury, and will show up as a ______ deflection
Posterior
positive
If current is moving away from V2 it is an _________ injury, and will show up as a _______ deflection
anterior
negative
Which lead has the biggest deflections overall? Why?
V4
Closest to the heart & close to 59 degree mean axis
V5 & V6 are progressively _______ than V4
smaller
further lateral on chest wall
What lead will not have an S- wave? Why?
Lead I
At the end of depolarization when the L lateral piece of the ventricle is depolarizing, the vector is now pointing more toward the (+) electrode in lead I
What lead will not have a Q-wave?
Lead III
T/F: When a ventricle is depolarized you will have a small vector
F
There is no current UNLESS THERE IS AN INJURY
You will have no vector & no current & all meters should read 0
What does a vector tell you?
- The angle tell you which way the current is going
The opposite direction of an injury as well - The size of the vector tells you how much electrical current is involved
What is a normal QT interval?
0.25 - 0.35 secs
What is another name for 3-leads?
Bipolar Leads
